Well, do they? Kevin Boyle gave a stimulating Grue Bag talk yesterday, which in part touched on the question whether absences, omissions and preventions can occupy the role of causes and effects in the causal nexus. In discussion we found ourselves quantifying over absences, though peer pressure prevailed in denying their existence at the same time. Such double-talk would have made Quine turn in his grave!
Here’s my proposal on how to admit quantification over absences with a clear conscience: paraphrase talk of absences in terms of relation-talk. What we need is a three-place relation between:
an absentee (the entity that’s absent),
locus1 where it’s absent, and
locus2 (that does not overlap locus1) where it’s present.
That’s my basic proposal for explicating absence-talk in terms of relation-talk, eliminating the former in favor of the latter. Absence-talk in counterfactual and manipulationist accounts of causation will require a more complicated modification of the basic proposal, but you get the idea.
P.S., this basic proposal is inspired by the Nyaya system of philosophy, one of the six Brahmanical systems in India. The Nyaya philosophers admit absences into their ontology, which I find very curious. My impression is that they take absence as a binary relation between the absentee and the locus where it’s absent. But my further impression is that I’m probably misrepresenting and oversimplifying their account, and that a close study of the Nyaya position would be a fruitful, worthwhile endeavor.